When Stocks Move in Unison, Look Out

Many sectors are rising, and falling, together, which makes it tough for investors to beat the market, and could be an ominous sign.

We've all heard the phrase, "it's a stock picker's market," meaning that individual stock attributes trump the ebb and flow of the broad market. (One tends to hear it most frequently, of course, from stock pickers.) This month, the opposite seems to be true. A majority of sector indexes I follow look the same on the charts, and that means the market, not the fundamentals of individual stocks, is the key.

It also suggests that investors are on edge, as correlation tends to rise in an environment when macroeconomic...